In one kind of onboard communication systems, a signal is transmitted to a service center when it receives a burglar alarm signal from a burglar detection ECU. A wireless communication unit of this kind of onboard communication system is required to be always turned on so that the burglar detection ECU can detect burglary any time and send the burglar alarm signal to the service center whenever it has detected burglary. With this configuration, a battery may be exhausted when a vehicle is parked for a long time and a discharging period of the battery becomes long.
To protect the battery from exhaustion, a function for forcibly terminating power supply from a battery to ECUs is proposed in JP-A-2003-63330. A power supply ECU is connected between the battery and the ECUs for monitoring the amount of current flowing from the battery to the ECUs. It forcibly terminates power supply from the battery to the ECUs when the amount of the current exceeds a reference value.
Sending a burglar alarm signal may be more important than protecting a battery from exhaustion because the burglary is more harm to a user than the dead battery. The above-described function terminates power supply from a battery to a wireless communication unit even during transmission of a burglar alarm signal to a service center. As a result, the burglar alarm signal cannot be properly sent to the service center.